The present invention relates to a voltage equalizer for battery elements for equalizing terminal voltages of battery elements which constitute a battery or the like.
In general, a battery including a number of (for example, about one hundred) battery elements which are connected in series to each other is installed in an electric vehicle which is run by a motor or a hybrid vehicle which is run in combination of an engine and a motor. Then, a voltage equalizer is connected to the battery in consideration of securement of a charging capacity, extension of the life of each battery element and safety. Further, a voltage detector for detecting an abnormal terminal voltage of each battery element is also connected to the battery to eliminate a risk of the occurrence of a serious secondary failure which would be caused by heat and leakage of fluid which are caused in the event that there occurs a short circuit in one of the battery elements.
Conventionally, as a voltage equalizer of this type, a voltage equalizer for battery elements is known which was proposed by the applicant of the present invention and is disclosed in JP-A-2002-223528. In this voltage equalizer, a closed circuit is configured by battery elements of one of a plurality of groups of battery elements which are connected in series, each of a plurality of secondary windings which are magnetically connected to each other and each of one of pluralities of switching elements, and a closed circuit is configured by battery elements of the other group of battery elements, primary windings which are magnetically connected to the secondary windings in a common fashion and the other plurality of switching elements, whereby the output voltage of the one of a plurality of groups of battery elements which are connected in series is equalized by ON/OFF controlling the one of pluralities of switching elements and the other plurality of switching elements alternately.
In addition, as the voltage detector, a voltage detection circuit for battery elements is known which has already been proposed by the applicant of the present invention and is disclosed in JP-2002-357625. This voltage detection circuit is a voltage detection circuit for battery elements for detecting a voltage between terminals of each of a plurality of battery elements which are connected in series to each other which has a voltage detection means connected between terminals of each of the plurality of battery elements and adapted to cause a detection current to flow from an output terminal when a predetermined voltage is reached and a single detection signal output means connected via a load resistance to a negative terminal of a battery element, which is positioned on a minimum potential side, of the plurality of battery elements which are connected in series to the output terminal of the voltage detecting means, whereby a sufficient current for the single detection signal output means to output a detection signal can securely be allowed to flow even in the event that any of the battery elements reaches a predetermined voltage which is set in advance.
In the afore said conventional voltage equalizer (and the voltage detector), however, there exist the following problems to be solved.
As a first problem, when paying attention to the voltage equalizer, since energy is temporarily stored in the transformer and thereafter, a substantial equalization process is carried out, there still remains a room for improvement from equalization capability and equalization efficiency (equalization time) perspectives. In addition, since an equalization process is performed between all of the battery elements, respectively, there exists a risk that excessive charging and discharging currents are generated in case terminal voltages between the battery elements vary largely.
As a second problem, in a case where the voltage detector is connected in addition to the voltage equalizer, since they constitute two dedicated devices which are independent from each other, a configuration is generated in which the two dedicated devices are combined with the battery elements, and this calls for increase in cost, enhancement of energy loss and enlargement of size of the entire system.
As a third problem, when paying attention to the voltage detector, since the terminal voltage of each battery element is detected through an independent detection circuit, a number of detection circuits which corresponds to the number of battery elements are required, and in case the number of battery elements is increased, this calls for an increase in components cost in conjunction with a remarkable increase in the number of components and an increase in production costs in association with the complexity of circuits. In addition, the size of the system is also increased, and this constitutes a cause for the prevention of the effort to save space in an electric vehicle where components layout space is limited, and wasteful energy loss is also increased.